Method of liquid electrostatic developing



United States Patent 3,411,937 METHOD OF LIQUID ELECTROSTATIC DEVELOPING Jerome Roteman, Freehold, NJ and Beatrice Arnowich,

New York, N.Y., assignors to Interchemical Corporation, New York, N.Y., a corporation of Ohio No Drawing. Filed Mar. 1, 1965, Ser. No. 436,329

Claims. (Cl. 117-37) ABSTRACT OF THE DISCLOSURE A method of liquid developing of negatively charged images employing a positively charged developer composition comprising a dispersion of a pigment in an electrically insulating liquid containing a resinous mixture consisting of linseed oil, rosin, and the reaction product of polyterpene and phenolformaldehyde, and having dissolved therein a metallic soap and a zirconium complex salt.

This invention relates to electrostatic printing and copying. More particularly, it relates to a method of developing electrostatic images using an improved liquid developer.

One typical conventional electrostatic printing process includes coating a surface of a relatively conductive backing member with a photoconductive insulating material such as selenium, anthracene, or sulfur, and then providing an electrostatic charge of a given potential on the surface of the photoconductive coating. Then, a light im age is focused on the charged surface discharging or lowering the potential of the irradiated areas, while leaving the remainder of the surface in a charged condition, thereby forming an electrostatic image. The electrostatic image may be rendered visible by the application of developer liquid or powder which is held electrostatically in the charged areas in the case of positive images, or, in the case of reversal type images, the charge on the developer is such that the developer is repelled from the charged areas and deposits in discharged areas. The developed image is then transferred and fixed to another surface. A more detailed description of such a conventional process may be found in US. Patent No. 2,297,691 to C. F. Carlson. A variation in the electrostatic printing process in which the intermediate step of transferring the developed image is eliminated and the developed image is produced directly upon the desired surface is described in US. Patent 3,052,539 to H. G. Greig.

We have now found an improved method of liquid developing of negatively charged electrostatic images which are the standard electrostatic images in the pr0cesses described above. Our method is particularly effective in the direct image method of electrostatic printing described in the Greig patent. The method may be considered to be an improvement over the conventional methods of liquid developing described in 2,907,674 to Metcalfe et al.

Metcalfe et al. teach developers containing linseed oil can be used only as negatively charged developers for the developing of positively charged images. We have now produced novel positively charged developers containing linseed oil for the developing of negatively charged images. In addition to linseed oil, our developers contain rosin, a terpene-phenolic resin which is the reaction prod- 3,411,937 Patented Nov. 19, 1968 net of polyterpene and phenol-formaldehyde resin, a metallic soap and a zirconium complex salt of the following formulation:

where n is a fraction between 1 and 2. The pigment and resinous material are dispersed in an electrically insulating liquid while the metallic soap and the zirconium complex salt are dissolved in said liquid.

The electrically insulating liquids used are the same as those described in the Metcalfe patent and conventionally used in the liquid developing art. The liquids have a high volume resistivity e.g., toluene, cyclohexane, perchloroethane, Freons (a trade name of E. I. du Pont de Nemours & Co. for various fluorinated compounds) n-pentane and carbon tetrachloride. While the examples which follow, use an aliphatic solvent having a boiling range of 315- 350 F., any of the conventional electrically insulating solvents will be operable in the method of this invention.

By metallic soaps, we mean metallic, especially alkaline earthand heavy-metallic salts of fatty acids containing at least 67 carbons and including naphthenic acid which is a cyclic aliphatic acid. Among the preferable soaps in the practice of this invention are the salts of naphthenic and octanoic acids including copper, cobalt, magnesium, manganese, iridium, cadmium, silver, potassium, titanium, cerium, zirconium, lithium and nickel naphthenates as well as zirconium, ferric, sodium, zinc, cobalt, silver, p0- tassium, cadmium, manganese and magnesium octoates. The terms octanoic acid and octoates as used in this description are meant to be broad enough to respectively cover the eight carbon 2-ethyl hexanoic acid and 2-ethyl hexanoates. Other metallic soaps such as lead, cobalt or manganese tallates, soyates or linoleates may also be used.

Modified rosins may be used in place of rosin, e.g., fumarated and maleated rosin, gum esters or glycerine modified-rosin as well as pentaerythritol modified rosin and phenol-formaldehyde modified rosin which is the reaction product of rosin and phenol formaldehyde.

The pigments may be any of the pigments used in the Metcalfe et al. patent.

It should be noted that unless otherwise stated in the specification and claims, all proportions are by weight.

For best results, it is very preferable that from 0.3 to 0.8 part of zirconium, in the form of are added for each part of pigment used and that from 0.5 to 2.0 parts of the resinous mixture are used for each part of pigment used. By the resinous mixture, we mean the combination of linseed oil, rosin and the polyterpene phenol-formaldehyde reaction product. Preferabl the linseed oil constitutes from 30 to and most preferably from 50 to 75% of the resinous mixture. The metallic soap preferably is present in small amounts so that the metal present is equal to about from 0.4 to 2% of the resinous mixture.

The following example will illustrate the practice of this invention:

3 Example The following ingredients are mixed:

Grams Rosin 1.0 Rosin modified with 15% phenol formaldehyde 0.9

The resulting mixture is then mixed with 80.3 grams of a solution of C4H CH(C2H5)C0O( rO)nOC(C2H5)HCC4H9 in mineral spirits (solids content 28% and zirconium content 6% by weight), 270 cc. of Xylene and 3,330 cc. of an aliphatic hydrocarbon solvent having a boiling range of 315350 F. and a K.B. value of 27. A black dispersion is formed.

Then an electrostatic copying sheet prepared in accordance with Example 1, US. Patent No. 3,052,539 is charged negatively by subjecting it to a corona discharge and then exposed to a light image to produce a negatively charged electrostatic image on the surface of copying sheet in accordance with the procedure of Patent No. 3,052,539.

In an attempt to develop the electrostatic image into a visible image, the copying sheet bearing the charged image is submerged in the above dispersion for about 6 seconds. A sharply defined black image is formed. It is clear and readable.

The developer composition of this example is left exposed to the atmosphere for a period of from one to three weeks and tested again in the above procedure. Images of substantially the same clarity and intensity are produced.

We claim:

1. A method of electrostatic printing comprising applying to a surface carrying a negatively charged electrostatic image, a positively charged developing composition comprising a dispersion of a pigment in an electrically insulating liquid containing from 0.5-2.0 parts by weight of a resinous mixture per part by weight of pigment, said mixture comprising 55 parts by weight of linseed oil, 22 parts by weight rosin, and 23 parts by weight of the re action product of polyterpene and phenol-formaldehyde and having dissolved therein from 0.42% based on resinous mixture present of metal in the form of a metallic soap and from 0.3 to 0.8 part by weight of zirconium per part by weight of pigment, in the form of where n is a fraction between 1 and 2.

2. The method of claim 1 wherein said rosin is a modified rosin formed by the reaction of rosin with phenolformaldehyde.

3. The method of claim 1 wherein said metallic soap is manganese naphthenate.

4. The method of claim 1 wherein said metallic soap is cobalt soyate.

5. The method of claim 1 wherein said metallic soap is a mixture of aluminum octoate, manganese naphthenate and cobalt soyate.

References Cited UNITED STATES PATENTS 2,584,041 1/1952 Nowak et al. 106310 2,739,905 3/1956 Mack et al. 106'310 2,793,962 5/ 1957 Collins et al. 106-310 2,807,553 9/1957 Fischer 106310 2,907,674 10/ 1959 Metcalfe et a1 1l737 3,102,045 8/ 1963 Metcalfe et al. 1l7--37 3,141,793 7/1964 Oliphant 11737 3,215,527 11/1965 Johnson 11737 3,220,830 11/ 1965 Kashiwabara 25262.1 3,231,374 1/1966 Sciambi 11737 3,241,957 3/1966 Fauser et al. 117-37 3,251,688 5/1966 Mihajlov 11737 3,259,581 7/1966 Matkan 11737 3,320,169 5/1967 East et al 252--62.1

" WILLIAMD. MARTIN, Primary Examiner.

EDWARD J. CABIC, Assistant Examiner. 

